Environmental Science & Engineering - www.esemag.com - September 2002
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Nanofilters convert river flow into safe drinking water

Project manager Arnaud Douveneau, Vivendi, is counting on a new type of membrane in the nanofiltration plant in Méry-sur-Oise.

The world's first and largest nanofiltration plant for treating river water is located in Méry-sur-Oise, north of Paris. The plant is fully automated and the CIP (clean in place) loop for cleaning the membranes runs without virtually any manual intervention. Trouble-free CIP operation is ensured by, among other things, 30 plastic-lined magnetic drive pumps for dosing and conveying the chemicals.

Water supplies to the French public are mainly in the hands of private companies. A large share of the market is served by Vivendi, which was founded in 1853. In the north of Paris, the Syndicate des Eaux d'Ile de France (SEDIF) supplies 39 communities (800,000 inhabitants) from a plant that employs a new and very unique method of treating water from a river source. Located in Méry-sur-Oise, the treatment plant needed to increase production capacity. To do this, SEDIF decided to adopt a technology which had never been used before to treat river water: nanofiltration.

Nanofiltration is a membrane liquid separation technology that is positioned between reverse osmosis (RO) and ultrafiltration. While RO can remove the smallest of solute molecules, in the range of 0.0001 micron in diameter and smaller, nanofiltration removes molecules in the 0.001 micron range.

Nanofiltration is essentially a lowerpressure version of reverse osmosis where the purity of product water is not as critical as pharmaceutical grade water, or the level of dissolved solids to be removed is less than what is typically encountered in brackish water or seawater. As such, nanofiltration is especially suited to treatment of well water or water from many surface supplies like rivers or lakes.

Nanofiltration is used where the high salt rejection of reverse osmosis is not necessary. Yet nanofiltration is still capable of removing hardness elements such as calcium or magnesium. Like RO, nanofiltration is also capable of removing bacteria and viruses as well as organic-related colour without generating undesirable chlorinated hydrocarbons and trihalomethanes (THMs). Nanofiltration is also used to remove pesticides and other organic contaminants from surface and ground waters to help ensure the safety of public drinking water supplies.

Sometimes referred to as "membrane softening", nanofiltration is an attractive alternative to lime softening or sodium chloride zeolite softening technologies. And since nanofiltration operates on lower pressure than does RO, energy costs are lower than for a comparable RO treatment system.

Abridged from the Print Edition

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